The present invention relates to a voltage-to-current converting circuit which converts an input voltage to an output current.
In order to convert a voltage difference applied as an input into a change in a current, an emitter-degenerated amplifier is in general used. In this emitter-degenerated amplifier, the emitters of a pair of input transistors are connected through a conversion resistor both ends of which are connected to ground via constant current sources. In such a converting circuit, when an output current flowing through the conversion resistor is small, the output current is proportional to the difference of input voltages applied to the bases of the input transistors. However, when the output current increases, the magnitude of the output current cannot be ignored with respect to a bias current supplied by a constant current source, so that the output current does not become proportional to the difference of input voltages. In other words, when the difference of the input voltages become large, the output current will involve an error.